Wet spinning process



H. M. HOXIE 2,577,763

WET SPINNING PROCESS Dec. 11, 1951 Filed Nov. 5, 1949 H0 WARD M. HOX/E 4TTOR/YE X Patented Dec. 11, 1951 2,577,763 wE'r SPINNING raoosss HowardM. Hoxie, Chester, Pa., assignor to American Viscose Corporation,Wilmington, Del., a

corporation of Delaware OFFICE Application November 5, 1949, Serial No.125,679

. 1 v This invention relates to improvements in the production ofsynthetic or artificial fibers, films, or other shaped articles by thewet-spinning or wet-forming process.

In wet-spinning or wet-forming, as conventionally practiced, a solutionof the material to ing material which is an extractive for the extrusionsolvent but chemically inert to the fiber or film-forming material.Thus, in wet-spinning fiber-forming acrylonitrile polymers, includingpolyacrylonitrile and certain copolymers of acrylonitrile, improvedresults are obtained by spinning a dimethylformamide solution of thepolymer into a setting medium consisting of water and dimethylformamidein controlled predetermined proportions, as disclosed in my pendingapplication filed November 2'7, 1948, Serial No. 62,413.

The present invention is concerned more particularly with wet-spinningor wet-forming processes in which a solution or dispersion of the fiberor film-forming material is extruded into a setting medium comprisingthe solvent and a precipitant for the fiber-forming material whichprecipitant extracts the solvent or dispersing agent used in theextrusion, and has as one object to automatically maintain thecomposition of the setting medium constant or substantially constantfrom the beginning to the end of the extrusion by the addition theretoof liquid obtained by washing the article with a medium comprising theprecipitant.

In accordance with the invention, the solution or dispersion of fiber orfilm-forming material is extruded into a setting medium consisting of apredetermined proportion of the extrusion solvent or dispersing agentand a predetermined proportion of a liquid which is a precipitant forthe fiber-forming material and an extractive for the extrusion solventor dispersing agent but '13 Claims. (CI. 18-54) ture of the precipitantand a minor proportion of the solvent or dispersing agent, to removesolvent or dispersing agent carried out of the bath from the fibers, andliquid from this initial washing of the, article is delivered directlyto the setting bath. The liquid resulting from the initial washingconsists of a mixture of the extrusion solvent or dispersing agent andthe precipitant, i. e., a mixture the constituents of which are the sameas the constituents of the setting medium. By controlling the amount ofwash liquid added to the setting bath, and the proportion of solvent ordispersing agent mixed with the precipitant in that liquid, if a mixtureof the two is used for washing the article, taking into. account theamount 0! solvent or dispersing agent introduced into the bath duringthe extrusion, the composition of the setting medium is automaticallymaintained substantially constant from the beginning to the end of theextruding operation, the composition being automatically andcontinuously adjusted by the introduction of the liquid from the washingstep.v It is unnecessary, therefore, to withdraw the bath from thevessel in which the extrusion is performed, in order to refresh 'itwithdrawal from the setting bath. This may also be the final washing, orthe article may be subjected to one or more further washings with theprecipitant if it retains residual extrusion solvent. I

In some cases, extrusion solvent or dispersing agent remaining in" or onthe article after initial washing thereof may be removed by heating thearticle to volatilize the solvent or dispersing agent which ischemically inert to the fiber or filmforming material. to form thedesired shaped article, the article is withdrawn from the bath andwashed with the precipitant, or with a mixif the temperature ofvolatilization is belowthe temperature at which the article is damagedby heat. However, in the preferred embodiment, residual solvent ordispersing agent carried by the fibers after initial washing thereof isremoved by subsequent washing and cycled for mixing with the liquid tobe used in the initial washing step. The proportion of solvent ordispersing agent mixed with the precipitant in the liquid used in theinitial washing step is controlled so that the solvent'or dispersingagent in the liquid from the washing step plus the solvent or dispersingagent introduced in the extrusion and remaining in the setting mediumafter the fibers are withdrawn is sufllclent to maintain the relativeconcentrations of solvent or dispersing agent and precipitant in thesettin medium constant or substantially constant throughout theextrusion operation. All of the liquid from the initial washing may beadded directly to the setting bath or only a controlled portion thereofmay be added to the bath, depending on the amount of precipitant used towash the fibers and the amount of precipitant and solvent required to beadded to the bath to maintain the composition of the bath constant.

The method of the invention can be used for producing artificial orsynthetic fibers or other shaped articles from any fiber or film-formingmaterial which can be dissolved or dispersed and wet spun, when theshaping involves precipitation only, and the setting medium consists ofa mixture of the solvent or dispersing agent for the fiber-formingmaterial and a liquid which is a precipitant for the fiber-formingmaterial and an extractive for the extrusion solvent or dispersingagent. Examples of suitable fiber and filmforming materials are theorganic acid esters of cellulose, the fiber-forming synthetic resins,including polyamides, polyesters, fiber-forming vinyl resins, polyvinylalcohol, and fiber-forming polymers and copolymers of acrylonitrile.

The solvent or dispersing agent selected will depend on the particularfiber or film-forming material to be spun orv shaped. The precipitantwhich extracts the extrusion solvent or dispersing agent but which isinert to the fiber-forming or film-forming material will depend on boththe fiber or film-forming material and the solvent or dispersing agentin which it is dissolved or dispersed. As examples of suitable solventsor dispersing agents may be mentioned acetone for commercial, secondarycellulose acetate and such fiber-forming vinyl resins as those resultingfrom the copolymerization of vinyl chloride and vinyl acetate or ofvinyl chloride and acrylonitrile and containing from 40 to 55%acrylonitrile in the molecule; hot phenol or formamide for thepolyamides; chloroform for the polyesters; and dimethylformamide,dimethylacetamide or dimethylpropionamide for polyacrylonitrile oracrylonitrile copolymers containing from '10 to 98% by weight ofacrylonitrile in the molecule and obtained by copolymerizingacrylonitrile with one or more monoethylenically unsaturatedpolymerizable substances including vinyl acetate, styrene, vinylchloride, basic vinyl monomers such as the vinyl pyridines andparticularly 2-vinyl pyridine, isobutene, dimethylfumarate,methylmethacrylate, meihacrylonitrile, and acrylic acid and its esters.

The solvents and dispersing agents mentioned are illustrative only andother solvents or dispersing agents may be substituted for them.

The precipitant may be any liquid which is an extractive for theextrusion solvent or dispersing agent but inert to the fiber-formingmaterial. When water meets these essential requirements, water is thepreferred precipitant for use in the setting medium and as theprecipitant for use in washing the article.

A specific embodiment of the invention contemplates the production offibers or threads from solutions or dispersions of acrylonitrilepolymers, including polyacrylonitrile and copolymers containing from '70to 98% by weight of acrylonitrile,

in dimethylacetamide, by spinning the solution into a setting mediumconsisting of water and a controlled proportion of dimethylacetamide. Ina preferred embodiment, a. solution of the acrylonitrile polymer indimethylacetamide is continuously extruded into a setting mediumcomprising a mixture of water and dimethylacetamide containing thedimethylacetamide in a selected proportion between 20 and 70% by volume,and the composition 01' the setting medium is maintained constant bywashing the fibers withdrawn 'from the bath with water or watercontaining a minor proportion of dimethylacetamide, and directly addingall or a controlled amount of the liquid from the washing step into thesetting bath. The conditions are selected so that the composition of thesetting medium does not vary more than 2% from the predeterminedvolumetric proportions, and the proportion of dimethylacetamide is atleast 20% by volume.-

At the start of operations, under any given set of spinning conditions,the amount of liquid resulting from the washing of the fibers which mustbe directed into the setting bath, and the proportion of precipitant tosolvent required in that liquid, to maintain the composition of thesetting bath constant, can be determined by observation of therefractive index of the bath, and therein the amount of wash liquiddirected into the bath are generally not required, so long as thespinning conditions are not changed.

Suitable apparatus for the production of artificial or synthetic fibersor threads in accordance with the invention is illustrated in theaccompanying drawing in which Figs. 1 to 3 inclusive, are diagrammaticperspective views of various embodiments oi the invention.

Referring to Fig. 1, reference numeral 2 indicates a spirmeret throughwhich a solution of the dispersion of the fiber-forming material isextruded into the setting liquid comprising a mixture of the solvent anda precipitant for the fiberforming material, in selected proportions,contained in vessel 3. The fibers 4 are withdrawn from the bath andpassed upward through tube 5 to the squeeze rolls 8, 9. The tube 5 maybe of any suitable internal diameter and length and is I supported ininclined relation between vessel 3 and a tank or vessel 6 with its lowerend projecting into vessel 3 and its upper end communicatin with vessel6. Guides I!) and II are provided for guiding the filaments or yarn.Washing liquid comprising the precipitant is metered to tube 5 fromvessel 6 by pump 1 and fiows downward through the tube to vessel 3,countercurrently to the fibers advancing from the setting bath. Vessel 3is provided with an overflow pipe It for maintaining the bath atconstant level. Any liquid squeezed from the fibers between rolls 8, 9is caught in vessel 6. The fibers are passed to a washing drum l2 onwhich they are wrapped, a thread displacing guide I3 being providedadjacent to the drum, and the fibers are washed on the drum with washingliquid projected against the fibers through pipe l5 provided with valve[8 and consisting of the precipitant which comprises one constituent ofthe setting bath, or a mixture of the precipitant and a minor proportionof the solvent. The resulting wash liquid consisting of a mixture of theprecipitant and solvent is caught in the vessel I4 and cycled throughpipe I! to vessel 6. If necessary, the liquid from the washing can bediluted by addition of controlled amounts of the precipitant to vesselll or to vessel 6. A plurality of drums l2 and pipes l5 may be provided,the fibers being washed in successive stages whereby any residual 7solvent carried by the fibers after their initial washingin tube isprogressively reduced. The wash liquid obtained at these successivewashing stages, and'containing progressively reduced amounts of spinningsolvent, may be cycled back to the previous washing stages and to vessel6, or the liquid remaining after each washing may be cycled directly tovesel 6.

The angle of inclination of the tube with respect to vessel 3 and vessel6, the length and diameter of the tube, and th rate at which the washingliquid is metered to the tube, as well as the concentration of solvent,if any, in the liquid used to wash the fibers, affect the efiiciency ofthe washing. These conditions are selected so that the amount ofsolvent, if any, in the liquid used to wash the fibers and the amount ofsolvent removed from the fibers in tube 5, plus the amount of solventwhich remains in the setting bath when the fibers are withdrawn afterany given immersion length, is such that the relative proportions ofprecipitant and solvent in the setting medium are maintainedsubstantially constant.

Referring to Fig. 2, reference numeral designates a spinneret throughwhich the solution of fiber-forming material is extruded into thesetting bath contained in vessel 2| and consisting of a mixture of thesolvent and a precipitant for the fiber-forming material inpredetermined proportions. The fibers or threads 22 are withdrawn fromthe bath under guide 2|a and wrapped around the drum 23 and threaddisplacing guide 24. Washing liquid comprising the precipitant or amixture of the precipitant and a minor proportion of the solvent'isprojected against the fibers on drum 23 through pipe 25 provided withvalve 28. The mixture of precipitant and solvent resulting from thewashing is delivered to vessel 2| through funnel 21. The quantity ofwashing liquid projected against the fibers on the drum is controlled byvalve 26 so that the composition of the mixture of precipitant andsolvent delivered to the bath through the funnel 21 is such as tomaintain the relative proportion of precipitant.to solvent in thesetting medium constant, taking into account the amount of solventintroduced as spinning solution and remaining in the bath after thefibers are withdrawn. Vessel 2| is provided with an overflow pipe 28 formaintaining the setting bath at constant level. A

plurality of washing drums 23 and valve-controlled pipes 25 may beprovided, the fibers being washed in successive stages and the mixtureof precipitant and solvent or dispersing agent obtained at each washingstage being cycled to a preceding stage and ultimately to, the initialwashing stage.

In the embodiment illustrated in, Fig. 3, the fibers formed byextrudingthe spinning solution through the spinneret 29 into the settingmedium comprising a mixture of solvent and precipitant contained invessel 30 are withdrawn under guide 3| and passed to the'godets 32 and33, threaddisplacing guides 34 and 35 being supported adjacent to thegodets. Along the path of its advance to godet 32, the filamentarybundle or yarn is washed with liquid comprising the precipitant flowingto the bathfrom the vessel 38 provided with the angularly disposedopen-ended member or spout 31. The washing liquid is introduced tovessel 36 through conduit'33 at a rate greater than the rate at whichthe liquid fiows from the vessel through member 31, and flows out of thevessel 38 through the overflow pipe 33 to maintain the liquid levelconstant. An advantage of the present method. additional to that oi.maintaining the composition of the setting bath constant by the additionthereto of'liquidresulting from initial washing of the fibers, is thatthe spinning solvent is recovered from the setting bath, in which it ispresent in relatively high concentration, and does not have to berecovered from dilute mixtures obtained at later washing stages. If thefibers are subjected to one or more washings additional to the initialwashing, the liquid from such washing is delivered to the initialwashing stage.

In washing the fibers, the proportion of solvent. if any, admixed withthe precipitant used to wash the fibers must be controlled and shouldnot be greater than one-half the amount of solvent present in thesetting medium.

The fibers may be stretched prior to, during, or after the initialwashing, at temperatures which will depend on the particularfiber-forming material, and may or may not be after-stretched. Forexample, the freshly formed fibers of the acrylonitrile polymers may bestretched to 300% at temperatures up to 100 C., or they may be stretchedmore than 300% at temperatures above 100 C., and such stretching may bethe only stretch given the fibers, or they may be stretched up to 200 or300% at temperatures up to 100 C., and after-stretched at temperaturesabove 100 C., the after-stretching being performed before or after finaldrying of the fibers.

In the embodiment shown in Fig. 2, drum 23 may be replaced by athread-advancing, threadstretching reel, so that the fibers advancingover the reel are stretched concurrently with washing thereof. In theembodiment shown in Fig. l, the fibers may be stretched between thesqueeze rolls 8, 9 and drum I2.

If the acrylonitrile polymer fibers are to be simultaneously stretchedand heated to a temperature above 100 C., the godet or other stretch ata temperature up to 100 C. may be omitted, or the stretching attemperatures above 100 C. may supplement the stretch at temperatures upto 100 C. Stretching may be performed prior to initial washing of thefibers, concurrently with initial washing of the fibers, before or afterdrying of the washed fibers, or before or after removal of residualsolvent carried by the fibers after their initial washing. In treatingthe acrylonitrile polymer fibers it may be preferred to reduce theresidual solvent to less than 1.5% by weight prior to stretching them attemperatures above 100 C. However, the fibers can be stretched at theelevated temperatures after removal of a substantial portion of theresidual solvent, or immediately after initial washing. The latterprocedure may be preferred, if the filaments or yarns are destined to bereduced to discontinuous lengths. For instance, the yarns may bestretched at temperatures above 100 C. after their initial washing, andforwarded to a cutter or collected into a large multi-filament bundlesuch as a tow and converted directly from tow to top, the discontinuousfibers in either case being treated with a relaxing liquid, such as hotwater, when water is inert to the fibers, which shrinks and curls thefibers and extracts the residual solvent.

The following examples illustrate specific embodiments of the invention.

Example I Using the apparatus of Figure 1, filaments are formed byextruding a spinning solution comprising a homogenous mixture ofdimethylacetanh 7 ide and 18% by weight of a copolymer containing, inthe polymer molecule, 90% acrylonitrile and 10% 2-vinylpyridine byweight, through a spinneret having 44 holes each 0.004 inch in diameter,into a setting medium consisting of 67% dimethylacetamide and 33% waterby volume at a temperature of 30 C. The filaments are given an immersionof 8 inches, and as the yarn is withdrawn from the bath it is washedcountercurrently in tube with water metered to the tube at a rate of 0.5liter for each liter of dimethylacetamide introduced into vessel 2 asspinning solvent. The liquid from the washing step flows directly intovessel 3, whereby the composition or the setting medium is maintainedsubstantially constant. The yarn is stretched between godets into waterat 80-85 C., washed, and then dried on a revolving drum heated by steamat 20 p. s. 1., and stretched as itis passed through a tube containingsteam at 60 p. s. i. The yarn is twisted and permitted to shrink freelyin boiling water. The yarns are dense, transparent, and do not showvoids on microscopic examination. They are dyed a brilliant scarlet in abath containing 2%, on the yarn weight, of Wool Fast Scarlet G. Conc.under usual wool-dyeing conditions.

Example II Using the apparatus of Fig. 2, filaments are formed byextruding a spinning solution comprising a homogeneous mixture ofdimethylacetamide and 18% by weight of a copolymer containing, in thepolymer molecule, 90% acrylonitrile and 2-vinylpyridine by weight, intoa setting medium comprising 80% water and 20% dimethylacetamide, byvolume, at 30 C. The fllaments are given an immersion of 8 inches, andas they are withdrawn from the bath, as a yarn, they are wrapped aroundthe drum 23 and washed with water metered from pump 25 at the rate of 4liters for each liter of dimethylacetamide pumped into vessel 2| asspinning solvent. The yarn is stretched between godets into water at80-85 C., washed, and dried on a revolving drum heated by steam at 20 p.s. i. Thereafter, the yarn is stretched as it is passed through a tubecontaining steam at 60 p. s. i. The yarns contain small voids or bubblesand are dyed to a pale pink in a bath containing 2%, on the yarn weight,

01' Wool Fast Scarlet G. Conc.

Since certain changes in carrying out the invention may be made withoutdeparting from its scope, it is intended that all matter contained inthe foregoing description shall be interpreted as illustrative and notin a limiting sense. In the claims the terms solvent and .solution" areintended to include both true solvents and solutions as well asdispersing agents and dispersions or colloidal solutions or mixtures inwhich the fiber or film-forming material is substantially uniformlydispersed.

I claim:

1. A method of forming artificial and synthetic fibers and other shapedarticles which comprises continuously extruding a solution of thematerial to be shaped into a setting bath comprising a mixture of thesolvent and a liquid precipitant for the material, which precipitant isan extractive for the solvent, continuously withdrawing the shapedarticle from the setting bath to the atmosphere, continuously washingthe article, as it emerges from the setting bath and'above the level ofthe setting bath, with a stream of liquid flowing continuously anddirectly into the emerging from the bath, said washing liquid con-.

sisting of the precipitant, and, at most, a minor proportion of theextrusion solvent, and continuously correlating the relative proportionsof precipitant and solvent in the liquid flowing into the setting bathfrom the washing with the amount of solvent introduced into the bath bythe solution 01 the material to be shaped, to thereby maintain therelative proportions of precipitant and solvent in the setting bathsubstantially constant from the beginning to the end 01 the extrusion.

2. A method as in claim 1, wherein the material to be shaped is acellulose organic acid ester.

3. A method as in claim 1, wherein the material to be shaped issecondary cellulose acetate.

4. A method as in claim 1, wherein the material to be shaped is asynthetic resin.

5. A method as in claim 1, wherein the article is stretchedsimultaneously with washing thereof.

6. A method as in claim 1, wherein the material to be shaped is anacrylonitrile polymer containing, by weight in the polymer molecule, atleast 70% of acrylonitrile.

'7. A method as in claim 1, wherein the material to be shaped is acopolymer of acrylonitrile containing, by weight in the copolymermolecule, at least 70% of acrylonitrile.

8. A method as in claim 1, wherein the ma terial to be shaped comprisesa copolymer of acrylonitrile and a basic vinyl monomer containing, byweight in the copolymer molecule, at least 70% of acrylonitrile.

9. A method as in claim 1, wherein the material to be shaped comprises acopolymer of acrylonitrile and a vinyl pyridine containing, by 'weightin the copolymer molecule, at least 70% oi. acrylonitrile.

10. A method as in claim 1, wherein the material to be shaped comprisesa copolymer of acrylonitrile and 2-vinylpyridine containing, by weightin the copolymer molecule, at least 70% of acrylonitrile.

11. 'A method of forming synthetic fibers and other shaped articles froman acrylonitrile poly mer containing, by weight in the polymer molecule,at least 70% of acrylonitrile, which comprises continuously extruding asolution of the polymer in dimethylacetamide into a setting bathcomprising a mixture of water and dimethylacetamide containingdimethylacetamide in a selected proportion between 20 and 70% by volume,continuously withdrawing the article from the setting bath to theatmosphere, continuously washing the article, as it emerges from thesetting bath, and above the level of the setting bath, with a stream ofwater containing, at most, a minor proportion of dimethylacetamide andflowing continuously and directly into the setting bath countercurrentlyto the article emerging from the bath, and continuously correlating therelative proportions of water and dimethylacetamide in the liquidfiowing into the bath from the washing with the amount ofdimethylacetamide introduced into the bath by the polymer solution, tothereby maintain the relative proportions of water and dimethylacetamidein the setting bath substantially constant from the beginning to the endof the extrusion.

12. A method of forming synthetic fibers from an acrylonitrile polymercontaining, by weight in the polymer molecule, at least 70% ofacrylonisetting bath countercurrently to the article which comprises nin ly r d n a solution of the polymer through a spinneret into a settingbath comprising a mixture of the solvent and a liquid precipitant forthe polymer which precipitant is an extractive for the solvent,continuously withdrawing the fibers from the setting bath to a take-updevice supported above the level of the setting bath, continuouslywashing the fibers on the take-up device with a stream of liquidconsisting of the precipitant and, at most. a minor proportion of theextrusion solvent, so that the liquid flows continuously downwardly fromthe take-up device into the setting bath, countercurrently to the fibersadvancing to the take-up device, and continuously correlating therelative proportions of precipitant and solvent in the liquid fiowinginto the setting bath from the washing with the amount of solventintroduced into the setting bath in the solution of the polymer, tothereby maintain the relative proportions of precipitant and solventinthe setting bath substantially constant from the beginning to the endof the extrusion.

13. A method of forming fibers from an acrylonitrile polymer containing,in the polymer molecule, at least 70% by weight of acrylonitrile,

which comprises continuously extruding a solution of the polymer througha spinneret into a setting bath comprising a mixture of the solvent anda liquid precipitant for the polymer, which Number precipitant is anextractive for the solvent, continuously withdrawing the fibers from thesetting bath along an upwardly inclined confined path to a take-updevice supported above the level of the bath, at a point beyond thebath, continuously washing the fibers advancing from the setting bathwith a stream of liquid consisting of the precipitant and, at most, aminor proportion of the solvent, and fiowing continuously and directl,vinto the setting bath along the confined path and countercurrently tothe fibers advancing from the bath, and continuously correlating therelative proportions of precipitant and solvent in the liquid flowinginto the bath from the washing with the amount of solvent introducedinto the bath with the solution of the polymer, to thereby maintain therelative proportions of pre cipitant and solvent in the setting bathsubstantially constant from the beginning to the end of the extrusion.

HOWARD M. HOXIE.

REFERENCES CITED ['he following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date 2,236,648 Nagel et al Apr. 1, 1941

1. A METHOD OF FORMING ARTIFICAL AND SYNTHETIC FIBERS AND OTHER SHAPED ARTICLES WHICH COMPRISES CONTINUOUSLY EXTRUDING A SOLUTION OF THE MATERIAL TO BE SHAPED INTO A SETTING BATH COMPRISING A MIXTURE OF THE SOLVENT AND A LIQUID PRECIPITANT FOR THE MATERIAL, WHICH PRECIPITANT IS AN EXTRACTIVE FOR THE SOLVENT, CONTINUOUSLY WITHDRAWING THE SHAPED ARTICLE FROM THE SETTLING BATH TO THE ATMOSPHERE, CONTINUOUSLY WASHING THE ARTICLE, AS IT EMERGES FROM THE SETTLING BATH AND ABOVE THE LEVEL OF THE SETTLING BATH, WITH A STREAM OF LIQUID FLOWING CONTINUOUSLY AND DIRECTLY INTO THE SETTING BATH COUNTERCURRENTLY TO THE ARTICLE EMERGING FROM THE BATH, SAID WASHING LIQUID CONSISTING OF THE PRECIPITANT, AND, AT MOST, A MINOR PROPORTION OF THE EXTRUSION SOLVENT, AND CONTINUOUSLY CORRELATING THE RELATIVELY PROPORTIONS OF PRECIPITANT AND SOLVENT IN THE LIQUID FLOWING INTO THE SETTING BATH FROM THE WASHING WITH THE AMOUNT OF SOLVENT INTRODUCED INTO THE BATH BY THE SOLUTION OF THE MATERIAL TO BE SHAPED, TO THEREBY MAINTAIN THE RELATIVE PROPORTIONS OF PRECIPITANT AND SOLVENT IN THE SETTING BATH SUBSTANTIALLY CONSTANT FROM THE BEGINNING TO THE END OF EXTRUSION. 